This invention relates to a blood processing apparatus of hollow fiber type with a plurality of hollow fibers used for extracorporeal circulation of blood to effect dialysis, purification, gas exchange, etc. of blood.
This kind of hollow fiber type blood processing apparatus is extensively used as oxygenators and dialyzers. As an example, an oxygenator apparatus as shown in FIG. 1 is well known as an aid (ECMO: Extracorporeal Membrane Oxygenation) to an organic lung by extracorporeal circulation. This structure will now be described briefly.
Reference numeral 1 designates a hollow fiber bundle having a plurality of hollow fibers, through which blood flows. This hollow fiber bundle 1 has its opposite ends embeddedly secured to and supported by respective partitioning walls 2 which isolate, in a liquid tight manner, a blood processing chamber 3a and blood port zones 4a to be described later from one another such that the hollow fibers are open to the zones 4a. The periphery of hollow fiber bundle 1 is covered by a housing 3, while the opposite ends of the bundle 1 are covered by liquid port covers 4 which constitute part of housing 3. Housing 3 includes a cylindrical body 5 and mount covers 6 fittedly mounted on the opposite ends of the cylindrical body 5. The mount covers 6 are held in close contact with the periphery of partitioning walls 2, thus forming a blood processing chamber 3a in housing 3. Mount covers 6 are provided with gas ports 3b for supplying oxygen for gas exchange with blood. A flow path is formed in chamber 3a.
Each port cover 4 defines an inner conical blood port zone 4a flaring toward end face 1a of hollow fiber bundle 1, and it has a blood port 4b provided at its free end and extending along axis X--X of the hollow fiber bundle and a flange 7 provided at its flaring end. Blood port cover nut 8 having annular flange 8a is screwed on mount cover 6 of housing 3 such that annular flange 8a urges the outer surface of flange 7. Flange 7 is held in close contact via packing 9 with an edge portion of partitioning wall 2.
The oxygenator of this structure is of internal return flow type, and in which blood enters the hollow fibers from one blood port 4b and through one blood port zone 4a, and as it passes through the hollow fibers carbon dioxide gas in it is exchanged through the hollow fibers with oxygen supplied to blood processing chamber 3a from one gas port 3b. Blood gaining oxygen is returned to the organism through the other blood port zone 4a and the other blood port 4b. Carbon dioxide gas removed from blood is let to the outside from the other gas port 3b.
In the above prior art oxygenator, the area of end surface 1a of hollow fiber bundle 1 is considerably large compared to the area of blood port 4b. Therefore, the speed of blood flowing through blood port zone 4a is not uniform. More specifically, the speed of blood flowing into or out of the hollow fibers is high in a central portion of end surface 1a right underneath or right above blood port 4b because the flow is led directly to or from port 4b, while it is low in edge portion of end surface 1a because the distance to the port is increased. Therefore, in blood port zone 4a at the edge of hollow fiber bundle the flow of blood is very low so that a stagnant state results or, in some cases, is completely stopped. In such a case, precipitation of blood cells is produced in a peripheral portion of hollow fiber bundle 1. If this occurs, it undesirably leads to formation of thrombus and further clogging of hollow fiber bundle 1.
Further, in the oxygenator of vertical type as shown in FIG. 1, blood is caused to flow either downwardly from the upper blood port zone to the lower one or in the converse direction, i.e., upwardly. The stagnation of blood in blood port zone 4a is produced pronouncedly in blood port zone 4a on the inlet side in the case of the downward flow and one on the outlet side in the case of the upward flow due to the influence of the gravitational force. A solution to this problem is particularly desired.
To solve this problem, there have heretofore been proposed a structure, in which the peripheral wall of the liquid port zone has a curved surface based on a predetermined calculation, and a structure, which has a particular blood port zone shape such as a revolving flow type. Examples of such structures are disclosed in Japanese Patent Publications No.62-54510 and No.60-5308 and Japanese Patent Disclosure No.62-21107.
However, stagnation of blood can not be sufficiently prevented even with these proposed blood processing apparatuses. More specifically, where downward blood flow is caused, stagnation of blood in a peripheral portion of hollow fiber bundle still can not be prevented with the apparatus, in which the peripheral surface of the inlet side blood port zone has a curved shape based on a predetermined calculation, while with the apparatus of the revolving flow type it is produced in a central portion of the hollow fiber bundle although it is prevented in the peripheral portion.
Further, the proposed structures mainly aim at prevention of blood stagnation in the inlet side blood port zone which is particularly significant where downward blood flow is caused. That is, they neither aim nor provides for any expected effect of prevention of blood stagnation in the outlet side blood port zone which is particularly significant where upward blood flow is caused.
Particularly, with recent development of materials having compatibility to blood, non-heparin extracorporeal circulation without use of heparin or like agent against coagulation of blood is being tried. In this case, the stagnation of blood causes clogging of the hollow fiber bundle and formation of thrombus, and it is fatal if extracorporeal circulation is performed for a long time, thus posing significant quality and safety problems.
Further, in extracorporeal circulation using an oxygenator, it is usual in view of the arrangement of the blood circuit and priming operation and also in case of coupling a heat exchanger to the oxygenator, to dispose the apparatus vertically for causing upward blood flow from the considerations of the safety of a heavy and large heat exchanger filled with water. In such cases, therefore, the stagnation of blood in the outlet side blood port zone presents particular significant problems.
Further, where a centrifugal pump or like constant flow pump is used for upward blood flows, blood flow not pulsatingly but constantly, and therefore in the blood port zone blood stagnation is liable to be produced in the peripheral portion.
Further, this kind of blood processing apparatus has the following problems.
As blood processing apparatus where extracorporeal circulation is performed there are oxygenators and dialyzers, and for enhancing the effect of processing recirculating blood led out from the organism back to the blood processing apparatus is in considerable practice in therapeutical processes, in which CO.sub.2 in blood is removed by extracorporeal circulation. The recirculation is usually performed with a system as shown in FIG. 2(a), in which two reservoirs R1 and R2 and two pumps P1 and P2 are provided, or with a system as shown in FIG. 2(b), in which only two pumps P1 and P2 are provided, i.e., no reservoir is provided, in the recirculation circuit.
With the system with the reservoirs, however, a great amount of blood is circulated. Extracorporeal circulation without use of any anti-coagulation agent is also tried to prevent bleeding when the apparatus is used continuously for a long time. In this case, however, the system with the storage units can not be utilized because thrombus is formed in the stagnated part of the blood.
Further, even with the system without use of any storage unit, extreme pressure variations are liable depending on the timing of operation of the two pumps, and an increase of the amount of recirculation may produce a negative pressure in the outlet side blood port zone in the blood processing apparatus. This not only leads to rupture of blood cells, but if the hollow fiber film is porous, the possibility of introduction of air bubbles is increased, thus making it difficult to continue operation. Further, in the inlet side blood port zone an increase of the amount of recirculation may produce positive pressure, thus leading to the rupture of blood cells.
In order to prevent this, it is tried to hold the pumps in a non-occulusive state. In this case, however, reverse flow or idling is liable to be produced, making it difficult to grasp the amount of blood and also causing extreme damage to blood. Besides, doing so is hardly ineffective in the prevention of negative pressure generation.